In order to address the needs of the poor it is necessary to measure health behaviours and service uptake of poor people. However very little is known about these outcomes for the poorest of the poor. This is a key argument of an issues paper produced by the DFID Health Systems Resource Centre (HSRC) on behalf of the UK Department for International Development (DFID). The paper aims to review the existing methods and sources available to measure the health problems of the poor, their access to services, spending on health and mortality differentials, in order to advance the debate on how to build a strategy for systematically upgrading the evidence base in health.